The liquid crystal display element is used in various home electric appliances, measuring instruments, panels for automobiles, word processors, electronic notebooks, printers, computers, and televisions as well as clocks and calculators. Representative examples of a liquid crystal display system include a TN (twist nematic) type, an STN (super twist nematic) type, a DS (dynamic photo scattering) type, a GH (guest host) type, an IPS (in-plane switching) type, an OCB (optical compensation birefringence) type, an ECB (electric control birefringence) type, a VA (vertical alignment) type, a CSH (color super homeotropic) type, and an FLC (ferroelectric liquid crystal). Moreover, as a driving system, there are a static driving, a multiplex driving, a simple matrix system, and an active matrix (AM) system driven by a TFT (thin-film transistor), a TFD (thin-film diode) or the like.
In these display systems, an IPS type, an ECB type, a VA type, a CSH type, and so forth have a characteristic of using a liquid crystal material having a negative Δ∈. Among them, in particular, the VA-type display system by an AM driving is used for a display device, which requires a quick switching and a wide viewing angle, for example, a television or the like.
Low-power driving, a quick switching, and a wide operation temperature range are required for the nematic liquid crystal composition used in a display system such as a VA type. That is, it is required that Δ∈ is negative and its absolute value is large, the viscosity is low, and a transition temperature (Tni) of nematic phase-isotropic liquid phase is high. Moreover, from the setting of Δn×d, that is, the product of a refractive index anisotropy (Δn) and a cell gap (d), Δn of the liquid crystal material is required to be controlled in an appropriate range in accordance with the cell gap. In the case of applying the liquid crystal display element to a television and so forth, a quick switching is emphasized and therefore, it has particularly been required to have a liquid crystal material having a low viscosity (η).
Until now, characteristics of a liquid crystal composition have been improved by determining in various ways a compound having a negative Δ∈ with a large absolute value.
As a liquid crystal material having a negative Δ∈, a liquid crystal composition using liquid crystal compounds (A) and (B) with a 2,3-difluorophenylene skeleton (see Patent Literature 1) as shown below is disclosed.

Although the liquid crystal composition uses liquid crystal compounds (C) and (D) as a compound having a Δ∈ of almost 0, in a liquid crystal composition requiring a quick switching such as a liquid crystal television, a sufficiently low viscosity is not achieved by the above liquid crystal composition.

Meanwhile, a liquid crystal composition using a compound represented by formula (E) has been already disclosed. However, the composition is a liquid crystal composition with a low Δn and obtained by combining liquid crystal compound (D) above (see Patent Literature 2), or a liquid crystal composition (see Patent Literature 3) obtained by adding a compound (an alkenyl compound) having an alkenyl group in the molecule like liquid crystal compound (F) for improving response speed. Therefore, further investigation is needed to have both a high Δn and a high reliability.

In addition, although the liquid crystal composition using a compound represented by formula (G) has been already disclosed (see Patent Literature 4), because this liquid crystal composition is a liquid crystal composition containing a compound including an alkenyl compound like the liquid crystal compound (F), there has been problems like easy occurrence of (image sticking) or a display defect such as display unevenness.

The influence of the liquid crystal composition including an alkenyl compound on a display defect has been already disclosed (see Patent Literature 5). However, in general, when the content of an alkenyl compound decreases, η of a liquid crystal composition increases, making it difficult to achieve a quick switching. As a result, it was difficult to achieve both the suppression of display defect and the quick switching.
Accordingly, even if a compound with a negative Δ∈ value is combined with liquid crystal compounds (C), (D), and (F), it was difficult to have both a high Δn and a low η and also to develop a liquid crystal composition with a negative Δ∈ which has no display defect or a suppressed display defect.
A liquid crystal composition in which formula (A) and formula (G) are combined with formula (I) having Δ∈ of almost zero is disclosed (see Patent Literature 6). However, since extremely low pressure is employed for injecting a liquid crystal composition to a liquid crystal cell for a process of producing a liquid crystal display element, compounds with a low vaporization pressure are evaporated, and thus it is considered that the content thereof cannot be increased. For such reasons, as the liquid crystal composition has limited content of formula (I), it exhibits a high Δn but has a problem of significantly high viscosity. Thus, it has been required to achieve both a high Δn and a low viscosity.
